Electric meter probe



April 26, 1960 'R. ABRAMs 2,934,738

ELECTRIC METER PROBE Filed June 7, 1956 Thermionic Corporation, Cambridge, Mass., a corporation of Massachusetts Y f Application June 7, 1956, Serial No. 589,978l

2 Claims. (Cl. 339-7108) vThis invention relates to electric contact devices, and particularly of the probe type such as for temporarily connectmg a meter to a circuit terminal.

Objects of the invention are to provide an implement which canbe inserted into confined quarters selectively to make contact with small terminal elements, wires, sockets or the like.without danger of disturbing the circuit or of causing short circuits, to provide such a probe which has a slender probing head or tip that exerts a strong gripping action securely attaching itself to a terminal ,element upon release of an opening'component of the device, being self-clamping so that it need not be held gripped during its use-to provide such a probe which can be easily operated with one hand and enables the user to approach, initially nd, and firmly grip a terminal with a minimum of effort or groping-and to provide such an implement which is durable, positive and eicient in action, inherently safe regarding damage to insulated conductors therewithin, easy to assemble and disassemble,

. and inexpensive to manufacture.

Briey stated by way of a summary indicating its nature and substance, the invention introduces an implement of the above type which comprises a slender barrel conning an axially slidable plunger, the actuating end of which protrudes from one end of the barrel. The opposite, operative, end of the plunger carries jaws which protrude from the other lend of the barrel and these jaws have external tapering portions which when moved axially of the barrel in a direction to draw the tapering portions inwardly cause the jaws to close; A spring located within the barrel normally tends to move the plunger in a direction to hold the jaws clamped together as long as the actuating portion of the plunger which protrudes from the barrel is mentioned above, is not pressed against the force of the spring. Manual depression of this portion moves `the plunger and the tapered portions ofthe jaws outwardly from the barrel in opposition to the pressure ofthe spring so as to release them andhence to permit them to open. Release of the actuating portion permits the jaws to close. An electric cable is connected to theA plunger and the jaws and'extends'from the actuating end of' the probe for connection to an associated device such as a meter.

In another important aspect of the invention, the tips of the jaws are shaped to provide an essentially rounded and smooth pilot portion which either protrudes from a longer jaw over the other shorter jaw at the same time securing the terminal between the jaws, or is formed by bothjaws in which case one of the jaws has a transverse groove.

These and other objects, and aspects of novelty of the invention will appear from the following description of a typical embodiment thereof illustrating its characteristics. This description refers to a drawing in which Fig. 1 is a plan view of the probe with a portion intermediate its ends omitted;

Fig. 2 is a section on the longitudinal axis of the implement showing the jaws in elevation;

Patent C Fig. 3 is a fragmentary enlargement partly in section and partly in elevation of the implement, taken at the end from which the jaws protrude; v

Fig. 4 is a diametrical section taken transversely of the implement on the line 4-4 of Fig. 3; and

Fig. 5 is a View similar to Fig. 3, indicating a modication of the jaw tips.

The implement shown in the drawing has a long slender cylindrical barrel 10 of insulating material, for example a plastic such as polyvinyl chloride, bakelite, rubber or the like. Within the barrel 10 is slidably arranged a tubular plunger 12 of similar material, one end of which protrudes from the sleeve 10 and has fixed to its end a cap 14. The cap can be held in place frictionally, by threading, or permanently by cementing. The other end of the plunger sleeve 12, opposite the cap 14, has within the barrel an internally threaded portion 16, to which is screwed one end of a spindle 18 made of a suitable resilient and good conductive metal resistant to corrosion, for example a phosphor bronze. i

The spindle 1S extends from the inner end of the plunger 12 axially through the opposite end of the barrel 10 and has at that end externally of the barrel a head 20, at least a portion of which is of larger diameter than the inside diameter of the barrel or of a constrictor sleeve 24, made of metal or plastic material, and inserted into the head end of the barrel. The constrictor sleeve is not absolutelyvnecessary and the barrel itself, suitably shaped, can take its function. The sleeve 24 can be fixed in the barrel tube by knurling and press fitting it thereinto or by cementing. The constrictor sleeve can also be made of a plastic which can be joined to that of the barrel such as by press fitting or cementing.

The head 20 has towards the spindle portion a neck 22 which tapers from a diameter larger than the interior of the' sleeve.24 to the spindle diameter whichjis smaller thanhtha't of the barrel or sleeve. The head and neck are integral portions of the spindle and are split axially, forv example by a saw cut which Vextends beyond the neck into the spindle so as to divide the head and neck into two'substantially semi-conical jaws 28 and 30 supported in spaced relation b y the divided halves of the neck and spindle which are elastic enough to allow the jaws to betsqueezed together by pressure applied thereto and to return to their spaced position when the pressure is released. The jaws taper from the larger diameter of thetneck forwardly to a probing tip 31, the head as a whole constituting in essence a biconical body whose maximal diameter is slightly larger than that of the inside edge ofthe sleeve 24. j Y

. Longitudinal movement of the spindle 18 in the barrel in .one direction drawsthe tapering neck portions 22 into the sleeve 24 or the end of the 'barrel 10, as the case may be, so as Vt'oapply pressure substantially at right angles to the axis of the divided neck portions and hence to press the jaws together to cause them to grip any object placed between them, such as a terminal wire t as illustrated in Fig. 3. Movement in the opposite direction disengages the tapered portions from the sleeve or barrel, permitting the elasticity of the spindle to restore the jaws to their normal spread apart position, thereby to release the object gripped thereby.

Normally the jaws are held closed by a spring 32 placed within the barrel under compression with one end bearing against the inner end of the plunger 12 and with the other against the inner face of the sleeve 24 or of an abutment Within the barrel provided for this purpose if the sleeve 24 should be dispensed with. The spring 32 tends to shift the plunger toward the right and hence to draw the spindle 18 and its tapering neck portions 22 into the tube or barrel 24 so as to squeeze the asume jaws together. By applying pressure to the cap 14 in opposite direction the plunger is forced inwardly against the spring 32 and the neck portions 22 are then moved outwardly from the sleeve orbarrel 24 to permit Ythe jaws to open.

The inner end of the spindle -18is provided with lan axial recess 34 into which is soldered o-r otherwise fixed the bare end portion of an electric cable 36 'which extends through the plunger 12 and through a vslot 38'to the exterior of the implement for connection to a meter. Preferably the slot 38 extends to the end of the plunger tube so as to facilitate the assembly of the parts. The wire 36 remains straight during the entire assembly and is only bent into the `slot 38 just'prior to the application of the cap 14. In this manner any danger of injury to the cable is avoided; it will also be noted that the wire is not disturbed during operation, the distance between the soldered joint 34 and the slot 38 being constant.

As previously mentioned, the tip or nose 31 ofthe jaws is designed tovpermit the jaws to b-e v'thrusted into a position for gripping a given circuit element. In the embodiment according to Figs. 1 to 3 the jaw 28 is made somewhat longer than the jaw 30 and has at its extremity a rounded tip 40 which overhangs the tip of the lower jaw 30, providing in this way a leading or pilot end.

Instead kof the tip construction according to Fig. 3, with the bulbous tip 40 overhanging that of the other jaw 30, Va construction according to Fig. is sometimes preferable. In this modification, the lower jaw 130 has a groove 131 accommodating a lsubstantial cross-sectional portion of the conductor t whereas the upper jaw 128 is smooth. This modification is more positive than that according to Fig. 3, since the wire t cannot slide within the sawcut that separates the jaws. In either case, the rounded tip promotes an easy probing for the terminal.

To operate the above described probe, its tip is guided towards the terminal to which it is to be connected, one hand only being necessary for that purpose. Upon reaching the desired point, the cap 14 is pressed inwardly for example with the thumb of the holding hand, opening the jaws. The jaws are then placed on either side of the terminal, and the cap released whereupon the probe rmly grips the terminal and can be released, leaving both hands of the operator free. If the embodiment according to Fig. 5 is used and the terminal insertedinto groove 131, the connection is particularly positive Whereas the tip construction according to Fig. 3 permits initially probing movements with open jaws and with the nose covering the jaw gap, and upon contact with the terminal a wider area of possible contact while the nose 40 securely prevents escape of the terminal.

. It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall Within the scope of the appended claims.

I claim:

1. An electric probe comprising: a cylindrical barrel; normally separated jaws formed by slitting an essentially biconical body which is mounted within one end of the barrel for axial movement relatively thereto such that the circular edge of the barrel contacting a cone of said body varies the jaw separation upon axial relative movement of body and barrel, saw jaws being of unequal length the longer jaw having'a tip being approximately located on a longitudinal center linelaying in the plane of contact of the jaws when engaged; and means for biasing said body in axial direction; whereby the jaws and the barrel can be formed to constitute a probe of minimal diametrical extension and the jaw gap can be rotated relatively to the barrel. 1

2. An electric test test probe comprising: a cylindrical barrel of insulating material; a plunger tube of insulating material slidable axially within the barrel, protruding with one end from one end of the barrel, having a slit and a cap at said protruding end, and having an internally threaded portion at the opposite end within the barrel; a metallic spindle having a threaded portion at one endfor engaging said threaded portion of the plungler tube and extending with the other end through the opposite end of the barrel; a pair of jaws at said extending end of the spindle having two biconically tapered portions, Ythe diameter of the inner portion increasing to a Y vdiameter larger than that of the barrel and the outer por- 'tiondecreasing to form the apex lof a conical tip, said jaws being of unequal length, the longer jaw having a tip extending beyond and overlapping the end of the shorter jaw, Ysaid tip being rounded to constitute a pilot and the center of the rounded tip being approximately located on a longitudinal center line lying in the plane of contact of the jaws when engaged; a coil spring within the barrel between an abutment of the barrel and said threaded portions of the plunger tube and the spindle, said spring tending to move the plunger tube such as to draw said inner tapered portion of the jaws inwardly to the barrel thereby to close the jaws; and an electric conductor connected to said spindle and laterally extending therefrom through said plunger tube and said slit, below said cap, tothe exterior of the probe; whereby the jaws and the barrel constitute a tool of minimal diametrical extension, the jaws are electrically connected to the outside through the electric conductor, andthe jaws and the conductor can be rotated relatively to the barrel.

`References Cited in the ile of this patent UNITED STATES PATENTS 1,008,018 Cunningham Nov. 7, 1911 l1,869,181 Beck `luly 26, 1932 2,549,731 Wattley a Apr. 17, 1951 2,580,682 Kraft Jan. 1, 1952 Y 2,682,649 Blonder June 29, 1954 FOREIGN PATENTS 248,614 Switzerland Feb. 16, 1948 748,811 `Cireat Britain May 9, 1956 

